1. Field of the Invention
This invention relates to a method for preparing alkenylsilanes. More particularly, this invention relates to the preparation of alkenylsilanes by the reaction of a gaseous acetylenic hydrocarbon with a gaseous silane containing a silicon-bonded hydrogen atom in the presence of a hydrosilylation catalyst under conditions that maximize the yield of the desired alkenylsilane and minimize both undesirable by-products and the hazards associated with processing gaseous acetylenic hydrocarbons.
2. Description of the Prior Art
It is known to prepare alkenylsilanes in general and vinyl silanes in particular by the reaction of an acetylenic hydrocarbon with a silane containing a silicon-bonded hydrogen atom, referred to hereinafter as an SiH-containing silane. This reaction can also produce appreciable amounts of the corresponding disilyalkane from the further reaction of the alkenylsilane with additional SiH-containing silane. U.S. Pat. No. 3,793,358, which issued to Bauer et al. on Feb. 19, 1974 discloses that formation of the disilylalkane can be avoided by conducting the reaction of an acetylenically unsaturated hydrocarbon and a silane containing one or two silicon-bonded hydrogen atoms in the presence of a platinum-containing hydrosilylation catalyst and a diluent consisting essentially of the disilylalkane that would be produced as a by-product of the reaction. The reaction is conducted at a temperature of from 120.degree. to 220.degree. C. and under a pressure of from 0.1 to 5 atmospheres gauge, equivalent to an actual pressure of from 1.1 to 6 atmospheres, and the alkenylsilane produced as a product is continuously removed from the reactor as a gas. In all of the examples a gaseous mixture of the acetylene and the silane is bubbled into the lower end of a tower that is partially filled with the disilylalkane and the catalyst.
U.S. Pat. No. 3,404,169, which issued to Gaignon et al. on Oct. 1, 1969 teaches preparing vinylsilanes by the reaction of acetylene with a halosilane containing a silicon-bonded hydrogen atom in the presence of a platinum catalyst and an inert liquid diluent such as an aromatic hydrocarbon under atmospheric pressure and reaction temperatures of from 80.degree. to about 120.degree. C. The examples of this application describe adding a mixture of gaseous acetylene and the silane reactant in liquid form through a tube that extends below the surface of a stirred mixture formed by blending chlorobenzene with finely divided platinum as the hydrosilylation catalyst. The present inventors discovered that the yield of the desired alkenylsilane produced under the conditions described in this patent is relatively low, and the reaction produces relatively large amounts of the aforementioned disilylalkane by-product.
U.S. Pat. No. 4,276,426 teaches a continuous process for hydrosilylation reactions catalyzed by chloroplatinic acid. In accordance with this process the reactants are continuously introduced into a tube type reactor wherein the contents are maintained at temperatures of from 120.degree. to 170.degree. C. The reactants are maintained in the liquid phase using superatmospheric pressure as required and are circulated at speeds of at least 1000 cm/minute. The exemplified ractants are esters of ethylenically unsaturated carboxylic acids and SiH-containing silanes. The conditions specified in this patent would not be suitable for acetylenic hydrocarbons, which would tend to decompose and/or react with explosive violence under these conditions.
U.S. Pat. No. 4,579,965, which issued to Kanner et al. on Apr. 1, 1986 teaches preparing vinyltri(t-alkoxy)silanes accompanied by only minor amounts of the corresponding bis(tri-t-alkoxysilyl)ethane by reacting acetylene with the corresponding organohydrogensilane in the presence of a platinum compound as the hydrosilylation catalyst at temperatures above 150.degree. C. A major disadvantage of this process is the chemical instability of the hydrosilylation catalyst at the reaction temperature. The catalyst is reduced to metallic platinum.
Japanese Unexamined Patent Publication No. 46,888/81, which issued on Apr. 28, 1981 discloses reacting a hydrogenhalosilane with from 8 to 20 moles of acetylene for each mole of the silane. This process requires recovery and recirculation of the large amount of unreacted gaseous acetylene to make the process economically practical and/or comply with environmental regulations governing discharge of hazardous acetylene into the atmosphere.
Japanese Patent Publication No. 133,296/81, which issued on Oct. 19, 1981 teaches using triphenylphosphine complexes of platinum, palladium or ruthenium as hydrosilylation catalysts for the reaction of acetylene with a monohydrocarbyldichlorosilane. Using triphenylphosphine complexes of specified group of platinum compounds is taught in Japanese Patent Publication No. 4,995/82, which issued on Jan. 11, 1982.
An objective of the present invention is to provide a method for the preparation of alkenylsilanes, particularly vinylhalosilanes or vinylalkoxysilanes that optionally contain 1 or 2 silicon-bonded hydrocarbon radicals. The process involves the reaction of an acetylenic hydrocarbon with an SiH-containing silane under conditions that yield only minor amounts of undesired by-products, particularly disilylalkanes, yet are not conducive to the explosive decomposition of the acetylenic hydrocarbon reactant.